Tonga (12) 22
Tries: Jennings, Vuna, Uaisele, Tonga Goals: Taufa'ao 2, Williams
Ireland (10) 20
Tries: Blanch 3, Platt Goals: Richards 2
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Highlights: Tonga 22-20 Ireland
A brilliant hat-trick from winger Damien Blanch was not quite enough as Ireland suffered a heartbreaking defeat by Tonga in their World Cup opener.
Tonga took a 12-10 lead into the break, but the drama came in the second half.
Pat Richards's touchline conversion of Blanch's third try put Ireland 20-18 in front with 12 minutes to go.
But a late score from winger Esikele Tonga put his side narrowly ahead, and they just about held off the Wolfhounds' desperate late challenge.
It was a hugely disappointing end for an Irish side that had been almost completely written off before the game, but Andy Kelly's team can be proud of a superb effort in Parramatta.
Tonga held on by the skin of their teeth after a classic encounter
The lead changed hands seven times in all as both sets of players refused to give an inch in an absorbing contest.
Ireland started full of enthusiasm, and were helped by referee Steve Ganson's interpretation at the ruck with Tonga conceding the first of a seemingly endless stream of penalties after just a few seconds.
But it was Tonga who opened the scoring, with the impressive Michael Jennings dancing past five Irish defenders to score next to the posts.
Ireland made life difficult for themselves by coughing up possession early in the tackle count on several occasions, and they were relieved to see Etuate Uaisele's score ruled out by the video official.
Tonga's indiscipline was a constant problem and Ganson finally lost patience after 24 minutes, sending Esikele Tonga to the sin-bin for yet another offence at the ruck.
Ireland took advantage, working an overlap on the right touchline for Blanch to flop over the line after a clever miss-pass from Scott Grix.
Michael Platt rounded off a fabulous Ireland move to put his side in front, although the final pass from Karl Fitzpatrick looked suspiciously forward.
Platt must have still been day-dreaming about his try a few minutes later though as Cooper Vuna took advantage of the full-back's indecisiveness to get his fingertips to a bouncing ball before a late penalty from Joel Taufa'ao gave Tonga a narrow advantage going into half-time.
Richards came close to scoring for Ireland just moments after the restart, only to knock on over the line after collecting a high kick out to his wing.
The two sides of Tonga's brilliant stand-off Feleti Mateo were in evidence soon after. First, he collected his own kick and produced an instinctive pass over his own head which almost resulted in a superb try.
But he followed it up by being sent to the sin-bin after back-chatting the referee once too often.
Again, Ireland rapidly took advantage with Blanch taking a magnificent Sean Gleeson offload for his second try of the game.
Ireland will have to pick themselves up for their next game against Samoa
Uaisele regained the lead for Tonga following great work from Tevita Leo-Lata and Epalahame Lauaki in the build-up, but Blanch responded with a classic winger's try in the corner after picking up Liam Finn's kick.
Richards booted over the conversion from the touchline and Ireland looked in good shape for an unexpected victory.
But Mateo produced a special play, kicking a 40/20 to set up the position from which Tonga scored to edge his side back in front.
And there was to be no fairytale end for Ireland, although they threatened through Blanch again and Ryan Tandy.
Tonga: Talanoa, Vuna, Jennings, Uaisele, Tonga, Mateo, Taufa'ao, Kaufusi, Leo-Latau, Manuokafoa, L. Paea, Fa'aoso, Manu. Replacements: Moa, Lauaki, Uasi, Williams.
Ireland: Platt, Blanch, Gleeson, Littler, Richards, Grix, Fitzpatrick, O'Carroll, Beswick, Tandy, Harrison, Doran, Finnigan. Replacements: McIlorum, Finn, Haggerty, Cassidy.